Project Summary/Abstract Pediatric high-grade gliomas are malignant brain tumors arising in children that are associated with very poor clinical outcomes. Indeed, treatment of diffuse intrinsic pontine glioma (DIPG), a pediatric glioma of the brainstem, has seen particularly little progress since its first description nearly a century ago. Recent efforts to profile the genetic alterations found in pediatric gliomas have revealed frequent mutations in histone H3 genes in these tumors, including lysine-to-methionine ?H3K27M? mutations in 80% of DIPGs. Tumors with H3K27M mutations, including DIPGs, possess somatic alterations in a variety of growth factor signaling pathways as well. Such co-alterations include activating mutations in the bone morphogenetic protein (BMP) pathway receptor ACVR1 and in the fibroblast growth factor (FGF) receptor FGFR1. Tumors with these mutations occur preferentially with H3K27M mutations in certain histone H3 variants and in specific regions of the central nervous system (CNS) for reasons that are not known. The roles of these mutations in tumorigenesis remain unclear; moreover, their potential values as therapeutic targets have yet to be fully explored. Because fresh tissue samples from patients are rarely available, an alternative human cell-based model is necessary to characterize these mutations in the context of pediatric gliomas. Human pluripotent stem cells (HPSCs) can be used to generate a variety of human cell types, including those of the developing CNS. HPSCs thus offer access to cells that are developmentally appropriate for pediatric glioma modeling, and are amenable to genetic perturbation for such studies. In order to gain insight into tumors harboring ACVR1 mutations and those harboring FGFR1 mutations with H3K27M, this study aims to build representative models of pediatric gliomas using a hPSC-based platform. Neural cells will be generated, mutations of interest will be introduced into these cells, and the cells will be tested for in vitro evidence of tumorigenic phenotypes. Xenografts will be used to establish in vivo models using transformed hPSC-derived cells. The cells and resulting tumors will undergo gene expression analysis as well as assays for changes to the chromatin landscape. These in vitro and in vivo models of ACVR1-mutant and FGFR1-mutant pediatric gliomas will then be used to screen small-molecule modulators of growth factor signaling pathways for compounds that might have therapeutic relevance and to validate compounds of interest. Studies using these new models will yield a greater understanding of the roles of H3K27M mutations and additional somatic alterations in pediatric gliomas, as well as how to counteract their effects for the benefit of patients.